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Interstellar Interlopers, Coming in from the great beyond
dudley
post Sep 15 2019, 02:48 PM
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Interesting that Borisov's Comet is considerably less reflective in the blue portion of the spectrum than are the examples given of known comets. These examples were presumably selected as the closest available match for the new interstellar interloper.
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HSchirmer
post Sep 17 2019, 12:06 PM
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Recent calculations suggest that we won't be able to get a probe to Borisov's Comet (Intersteller 2 aka "I2") with direct chemical rocket technology, but an Earth-Jupiter-Sun Oberth route should work.

QUOTE
The software shows that a mission with feasible Delta-V and direct transfer from Earth would have had to have been launched in July of 2018, using a Falcon Heavy launch vehicle, with arrival at the object in October of 2019.


The authors envision using the Oberth maneuver at the Sun in combination with a Jupiter flyby, thus leveraging the deepest gravitational wells available to us in the Solar System. The proposed trajectory is shown in the figure below, drawn from the paper. Notice that the Jupiter flyby is here used to decelerate the spacecraft toward the Sun. The Oberth maneuver at the Sun then flings the spacecraft outbound for its encounter with C/2019 Q4 (Borisov).

https://www.centauri-dreams.org/2019/09/16/...019-q4-borisov/


Well, thinking about a future "I3", perhaps a "high-speed storage orbit" ping-ponging a pair of probes back and forth between the Sun and Jupiter until they achieve extreme velocities, and wait for the next interstellar interloper. Figure two probes so that they're redundant, at opposite points of the orbit, allowing one to pursue an inbound encounter, the other to do an outbound study.
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fredk
post Sep 17 2019, 02:39 PM
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It's worth adding that the Jupiter-Sun route contemplates launch in 2030 and would arrive at the comet in 2045. Original source.
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HSchirmer
post Sep 18 2019, 04:34 PM
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QUOTE (fredk @ Sep 17 2019, 02:39 PM) *
It's worth adding that the Jupiter-Sun route contemplates launch in 2030 and would arrive at the comet in 2045. Original source.


Should clarify, that would be sending a cube sat to Borisov using an Oberth "Jupiter- Sun drop kick"
The authors seem to imply that a New Horizons class probe to 1I/’Oumuamua might still be possible.

The huge difference in probe mass is because 'Oumuamua is on a mostly ecliptic path, while Borisov is on a mostly polar path.


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stevesliva
post Sep 19 2019, 01:07 AM
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Gives an idea of how long these things are nowhere near stars to thing that our not-exactly-warp-speed probes could catch them. They'll next be within several AU of a star... not soon.
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HSchirmer
post Sep 19 2019, 02:21 AM
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QUOTE (stevesliva @ Sep 19 2019, 01:07 AM) *
Gives an idea of how long these things are nowhere near stars to thing that our not-exactly-warp-speed probes could catch them. ...


Well, with a Jovian-Solar slingshot, you leave 3 Solar radii at 362 km/sec and then coast and arrive at ~34 km/sec.

So, about 30 months to slingshot up to 0.001% of light speed and coast down to 0.0001% light speed.


How about 0.2% of light speed in 12 hours? Seems possible, as it uses existing science and materials.

QUOTE
A fully powered plasma magnet sail using a small nuclear power source could accelerate at 0.5G and reach 400-700 km/sec (0.2% of lightspeed) in half a day.
https://www.nextbigfuture.com/2018/01/plasm...-in-1-week.html
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Holder of the Tw...
post Sep 24 2019, 02:22 PM
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It's official now. Comet Borisov is now 2I/Borisov. Further updates to its trajectory leave no doubt that it is interstellar.

Minor Planet Center update link
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JohnVV
post Sep 24 2019, 06:19 PM
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For those using Celestia ( spice enabled ) i but together an add-on for this
see:
http://forum.celestialmatters.org/viewtopi...?f=18&t=973

i will need to rename it to "2I/Borisov" it is using the old name still
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HSchirmer
post Sep 24 2019, 11:40 PM
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QUOTE (JohnVV @ Sep 24 2019, 06:19 PM) *
For those using Celestia ( spice enabled ) i but together an add-on for this
see:
http://forum.celestialmatters.org/viewtopi...?f=18&t=973

i will need to rename it to "2I/Borisov" it is using the old name still


Excellent!
Thank you.
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antipode
post Sep 25 2019, 03:12 AM
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Kruger 60 (DO Cephei) system as a possible source system for 2I/Borisov

https://arxiv.org/pdf/1909.10952.pdf

P
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ngunn
post Sep 25 2019, 09:35 AM
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The following sentence is highlighted in that paper and seems to represent their central finding:
As a result we obtained that 1 Myr ago C/2019 Q4 passed double star Kruger 60 at a small distance of 1.74 pc having an extremely small relative velocity of 3.43 km/s.

It's not clear to me why we should be looking for such a recent origin for this object. Could it not have been ejected from its parent system at any time during the age of the Milky Way? Or am I missing something about the expected lifespan of small bodies in interstellar space?
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Hungry4info
post Sep 25 2019, 12:21 PM
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Nearby origins are a priori more favored over more distant origins, because in whatever event ejected the comet, the "aim" doesn't have to be as "good" to hit a nearby system as it does a more distant system. With nearer systems have a larger angular diameter, if Jupiter were to kick out an asteroid, it would be a lot higher chance that it would fly past Proxima Centauri than, say, OGLE-TR-56.


--------------------
-- Hungry4info (Sirius_Alpha)
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ngunn
post Sep 25 2019, 01:14 PM
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Indeed distant systems individually subtend smaller angles but they are more numerous in exactly the same proportion, so I'm not sure that argument holds. Also, Gaia notwithstanding, we are in no position to say where individual stars were nor how they were moving billions of years ago. Our solar system will have had a lot of different neighbours in that time that are now long gone. Once again the longevity of these small objects could come into play. Do they eventually wear away leaving just 'stardust'?
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tanjent
post Sep 25 2019, 03:16 PM
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If you were trying to guess the single star system with the highest probability of being the origin, then you would want to choose the system that subtended the largest patch of sky in the general direction the object came from. But under the assumption that these comet-like objects can last a long time and come our way from arbitrarily far away, and that we have no way to backcast the motions of individual star systems very far into the past, even the highest probability origin candidate is bound to be very unlikely. There might be some imaginable reasons for placing a low probability bet of this sort, for instance if we detected something very exciting about the candidate star system (must tread carefully here...) that would potentially justify the expense of launching a crash program to intercept the object. But for most practical purposes it will be wiser to avoid jumping to conclusions. It could easily have come from very far away, from any one of a large number of star systems.
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fredk
post Sep 25 2019, 04:03 PM
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It's worth noting that the authors estimate a closest approach of around 2pc to Kruger 60, which is only about 4pc away. That gives a closest approach of very roughly 25 or 30 degrees! So hardly a bullseye.

The close approach of 2pc seems on the large side for the object to have originated in Kruger 60's Oort cloud, especially given the small mass (less than half a solar mass) of the system. But the low velocity is suggestive.
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